Commercial and industrial buildings are typically constructed with flat or near flat roofs. Because these buildings do not have much if any of a pitch to the roof the collection of water on the roof surface resulting from rain and melting snow could present a serious structural load that could result in collapse of the roofs structure. To avoid this possibility most commercial and industrial building standards require that roofs of this type include drains positioned at locations that ensure that at least the majority of water accumulation may be removed from the roof through a drainage plumbing system.
Typical roof drains are installed on flat roofs by cutting a hole through the roof deck and installing a drain therethrough. The drain typically connects with drainage plumbing that carries the water away. The drain structure typically includes some form of flashing or collar that, through the application of sealant or other roof material prevents leakage at the site of the drain installation. These typical drain structures also include some form of drain ring and under deck clamping ring or structure that holds the drain in place and prevents its inadvertent removal or dislodgement from its installed position. The opening of the roof drain is typically covered by some form of grating or strainer structure to prevent the ingestion of large objects into the drain plumbing system. In most roof drain structures this strainer or grate takes the form of a hemispherical strainer to prevent or minimize the occurrence of obstruction of the roof drain through the accumulation of leaves and other debris that may accumulate on the roof.
Unfortunately, despite the inclusion of a strainer or other grating structure, many roof drains still become plugged or otherwise obstructed to the point that inhibits their ability to remove the accumulated water from the roof of the building. These obstructions can occur as a result of the collection of debris around or over the grate or strainer structure. Additionally, obstructions may also result in the roof drain system during winter months as a result of icing near the roof level of the open areas of the strainer. In addition to the obvious problems resulting from complete obstruction of the roof drains, minor obstructions that merely result in the reduction in the rate of water removal from the roof may also result in undo stress on the roof structure that may endanger its integrity. Additionally, even unobstructed roof drains may not be able to remove water at a rate to prevent its undue accumulation during periods of heavy storms and intense rainfall.
In recognition of the limitations of a single roof drain system, many building codes and many more contractors are installing backup roof drains connected to separate drainage system to ensure that the load carrying capacity of a roof structure is not exceeded if the primary roof drain system fails to remove the water accumulation at a sufficient rate. These backup roof drains are typically constructed in the same manner as the primary roof drains, but include a structure that prohibits the drainage of water through the backup drainage system until the level of the water reaches a predetermined depth. That is, the entry ports or slots on the backup roof drains are positioned at a height above the roof surface. This height is preferably chosen based upon the roof construction such that the weight of the water at that given height is well within the load carrying of the roof structure. The separate drainage system ensures that failure of the primary roof drain system due to an obstruction in the drainage system downstream from the roof drains will not affect the ability of the backup roof drain system to remove the water that accumulates above a given depth.
While the usage of a primary and backup roof drain system greatly enhances the safety of the roof construction, such also greatly increases the cost of the roof construction. This significant cost increase is a result of the requirement for essential double the number of roof drains that must be installed on the roof. Since typical primary and backup roof drains are of the same construction differing only in the strainer or inlet structure, the cost for such roof drains is essentially double. In addition to the increased cost necessitated by the purchase of twice as many roof drains, each roof drain requires a separate deck penetration or hole to be cut in the roof structure. This essentially doubles the labor cost associated with such a system as twice as many roof penetrations must be cut. Further, depending on the number of primary and backup roof drains that are installed, the overall structural strength of the roof may be weakened due to the large number of deck penetrations that are cut to accommodate both the primary and backup roof drains.
While these factors may be considered in the design of a new construction, and therefore compensated, the cost and structural impact to existing buildings that may wish to or are required to install such a backup roof drain system can be prohibitive. That is, on an existing building the roof's structure and strength are already set, and any impact thereto resulting from the installation of the backup roof drains is not easily compensated. Additionally, the roof surface itself may already be occupied by other equipment that limits the ability to properly position additional backup roof drains to maximize their effectiveness. Further, additional roof penetrations by other system within a building may also limit the ability to install the backup drains at appropriate locations due to clearance requirements dictated by the roof penetrations of the other systems. As a result, the retrofit of an existing building to install the backup roof drain system often is not only expensive but also quite problematic if it can be installed at all.
These problems are further exacerbated in areas that receive an abundant amount of precipitation. In such areas, the often rapid deposit of precipitation on the large area of a building's roof may not be drained away fast enough to keep up with a deluge. This situation often occurs even though the calculated flow from the numerous roof drains should be able to handle the amount of precipitation. The source of this problem relates to the Coriolis forces caused by the Earth's rotation. These forces result in a swirling vortex being formed around the drains, such as is illustrated in FIG. 1. As the flow enters the drain, the vortex is stretched and intensified. As a result, the convergence results in the buildup of a large static head over the drain (see FIG. 2), and ultimately limits the capacity of the drain far below its rated flow capacity.
Since many building specifications use the rated flow capacity of the drain pipe to dictate the number and size of the drains needed for a given roof, the existence of these forces and the limiting effect that they have on the water removal capacity of these roof drains can result in a dangerous buildup of water on the roof, especially during periods of heavy precipitation.
There exists, therefore, a need in the art for a means to reduce or eliminate the flow reducing effect of the Coriolis forces on drains, and on roof drains in particular.